Transducers have been widely used for converting the amount of a mechanical displacement into an electrical signal. It is known in the art, for example, to provide members which are manually rotated or slid, the amount of movement of such members providing a corresponding electrical signal. Among the known members of such kind are tuning or adjusting knobs for radio receivers and the operating handles for pinball machines.
In pinball machines in particular, if the player pulls the operating handle, the resultant amount of movement of the handle changes the voltage across a solenoid plunger. Since the speed of movement of the plunger varies with the value of the voltage across the solenoid plunger, it is possible to control the shooting speed of a ball. Thus, to aim the ball at a desired target on a playing field, the player imparts to the handle movement of a magnitude proportional to the force with which he wishes the ball to be shot. By contrast, if the amount of manipulation of the operating handle is less, then the ball is shot with a weaker force. in this way, the player obtains the desired propulsive force by adjusting the amount of his manipulation of the operating handle. Therefore, it is necessary for the transducer to have no play over the range within which the manipulation amount can be changed, and to maintain the correct correspondence between the manipulation amount and the propulsive force.
Conventionally, a variable resistor has been utilized for detecting the manipulation amount described above. Variable resistors, however, have a problem that their mechanical life is relatively short.
It might be thought that the conversion of mechanical movement into an electrical signal could be effected by using various types of optical transducers, for example, a pulse counter type transducer. But in order to achieve sufficient precision of the transducer, a high precision is required for the associated gear mechanisms or electronic circuits. As a result, the apparatus becomes expensive. Moreover, the optical transducer system necessitates taking countermeasures against foreign matter and dust. Therefore, there arose the problem that an inexpensive, simple, and highly reliable transducer was not previously available.